Irrigation systems such as center pivot irrigation machines frequently comprise a main pipeline section that is connected at its inner end to a fixed pivot where the water source is located, and a swing span that is connected to the outer end of the main pipeline section for watering corner portions of the field as the machine rotates about the central pivot. The main section typically comprises a number of pipeline spans supported by towers having non-steerable drive wheels that propel the system through the field. On the other hand, drive wheels on the tower of the swing span are usually steerable so as to permit the swing span to be steered along a particular path of travel during corner operations.
While watering a corner, the swing span swings through its arc at a different speed than the main section, and the correct speed for the swing span at any particular point in time depends upon the location of the swing span tower along its predetermined path of travel. In other words, the speed and location of the swing span tower must be closely coordinated with the speed of the main section, or else the swing span itself will undergo excessive compression or tension caused by relative movement, or attempted movement, between the main section and the swing span. The pivot joint between the swing span and the main section can also undergo excessive loading, leading to premature wear and failure.
It is known in the art to utilize such displacement of the swing span relative to the main section as a means for sensing the need to adjust the speed of the swing span. See for example U.S. Pat. No. 5,695,129 owned by the assignee of the present invention. See also prior U.S. Pat. Nos. 5,947,393 and 6,042,031 owned by Valmont Industries, Inc. wherein changes in the bowed configuration of the swing span, rather than linear displacement of the swing span, are sensed by a deflection sensor on the swing span to signal the need for a change in the speed of the swing span.
However, such prior speed control arrangements have not heretofore been available in a system having a “flow-through” joint wherein the water flow passage is coaxial with the joint pivot. Instead, such prior machines have typically utilized flexible hoses that by-pass the joint itself, leading from a point on the main section that is upstream from the pivot joint to a point on the swing span that is downstream from the pivot joint. Among other things, this has the disadvantage of limiting the maximum amount of rotation of the joint assembly because the flexible hosing that spans the joint has only a certain fixed length. Furthermore, the mere fact that an additional flexible hose is needed to transport the water around the joint presents a number of disadvantages.
The present invention provides a flow-through joint wherein the water inlet of the swing span and the water outlet of the main section are aligned vertically about the axis of joint rotation and which also permits a limited amount of displacement of the swing span relative to the main section for speed control or other purposes. It provides swing span displacement within the joint itself without sacrificing the flow-through nature of the joint or its range of motion in several directions. The permitted displacement is very slight, yet is of sufficient magnitude as to allow an appropriate control signal to be generated. The invention is particularly useful in machines wherein the drive motors for the swing span and main section are variable speed motors that operate continuously, as opposed to motors which stop and start periodically, although the invention has utility in those latter circumstances as well.
In a preferred form of the present invention, the flow-through joint has the upright, tubular inlet port of the swing span aligned axially with the upright, tubular outlet port of the main section and both disposed in concentric relationship with the upright axis of rotation of the joint. A turret is rotatably supported on the outlet port for free rotation about the joint axis. The inner end of the swing span is attached to the turret in such a way that the inlet port of the swing span remains in axial alignment with the outlet port of the main section in all rotary positions of the turret. At the same time, such connection permits a limited amount of generally linear or axial displacement of the swing span relative to the turret, which displacement can be utilized to carry out a control function such as speed control of the drive motors on the swing span. The connection between the swing span and the turret also permits a limited amount of up and down movement of the swing span relative to the main section without breaking the water-tight seal between the inlet and outlet ports at the joint.
In a preferred form of the invention, the turret has a pair of diametrically opposed coupling assemblies on opposite sides of the joint axis. A yoke on the inner end of the swing span has a pair of downturned arms that are coupled by the coupling assemblies to the turret. One of the coupling assemblies comprises a ball joint, while the other, opposite coupling assembly includes a component that is movable along a guide to a limited extent to permit displacement of the swing span. A pair of resilient but fairly hard cushions on opposite sides of the movable component prevent displacement unless the force applied thereto by the swing span exceeds a predetermined level, whereupon the movable component is allowed to move and mechanically operate a control arm that manipulates a rheostat, switch or the like in a control box. A flexible sleeve encompasses the inlet and outlet ports of the joint and maintains a fluid-tight seal at that location notwithstanding a slight horizontal twisting in the joint during displacement of the swing span and cocking or skewing of the ports during up and down movement of the swing span caused by changes in terrain.